INTEGRATED AIRBORNE IFSAR MAPPING SYSTEM
Ming Wei and Tim Coyne
Intermap Technologies Corp., 1200, 555-4th Avenue S.W., Calgary, Alberta, Canada T2P 3E7 -
mwei@intermap.ca and tcoyne@intermap.com
Commission I, WG 1/2
KEYWORDS: Synthetic Aperture Radar (SAR), Interferometry, IFSAR, DEM, GPS/INS, Airborne gravity system, Geoid
ABSTRACT:
A Digital Elevation Model (DEM) is fundamental information for the geo-spatial data infrastructure framework. Many applications
require three-dimensional (3-D) geo-spatial data with high spatial resolution and accuracy. One leading technology of the nationwide
3-D mapping is airborne interferometric SAR mapping system due to its all-weather acquisition capability. Compared to other
airborne mapping systems, the other advantage of the IFSAR mapping system is the efficiency. Flying at an altitude of 10 km, the
Intermap IFSAR system can map an area of 10000 to 20000 km2 per flight. The airborne IFSAR system consists of synthetic
aperture radar sensor with two radar antennas and the GPS/INS components. The radar pulse signals are collected from two radar
antennas and compressed by digital match filtering to extract the interferometric phase information. The GPS/INS system can
provide highly accurate position and orientation information. Combining the SAR interferometric information and the GPS/INS
navigation results the ortho-rectified radar image with 3-D information can be obtained. Based on the GPS/INS components of the
IFSAR system a new airborne gravity and geoid mapping system is developed by Intermap. The regional geoid undulation can be
determined by the airborne gravity system and the ellipsoid height is transformed to the orthometric height directly from the
integrated IFSAR system. Thus the integrated IFSAR system can simultaneously provide both sea level referenced DEM data and
gravity field information. This opens the application of IFSAR DEM mapping in the rural and mountain areas where accurate gravity
data and geoid are not available.
1. INTRODUCTION
Airborne Interferometric Synthetic Aperture Radar (IFSAR or
INSAR) technology attracts much attention in the geospatial
community over the last decade. Advantages associated with
airborne IFSAR mapping include flexibility of system
deployment, near weather-independent operation, cloud
penetrating capability, versatile map products, and quick turn
around time. Leaders in the geospatial community are gradually
realizing that airborne IFSAR is emerging as a complementary
or competitive cost-effective 3-D mapping technology which
mainly provides digital surface models (DSM), digital terrain
models (DTM), and orthorectified radar imagery (ORI).
The new development of Intermap IFSAR system focuses on
the two major issues: enhance the system efficiency and
improve the mapping accuracy. This can be achieved by
improving the data acquisition process, the IFSAR processing
algorithm including GPS/INS integration algorithm and the
calibration method.
For the 3-D mapping applications, accuracy is one of the most
important performance indicators of the IFSAR system. In this
paper, a detailed error model of 3-D SAR image and DEM is
presented for an analytic assessment. The comparison of the
IFSAR DEM to external DEM data demonstrates that the
accuracy of 0.5 - 1.0 m of DEM can be achieved by the
Intermap IFSAR mapping system.
The DEM height based on the GPS solution is normally referred
to the ellipsoid. To obtain the orthometric height the accurate
geoid undulation is required. Based on the GPS and IMU
components of the IFSAR system, Intermap has developed an
airborne inertial gravity system to extract the gravity
disturbance information from highly accurate IMU
measurements. Using the gravity information the precise local
or regional geoid over the flight area can be determined. By
using a global geoid model, such as EGM96, the accurate
absolute geoid with adequate resolution is determined and the
ellipsoid height is transformed to the orthometric height. The
mapping products of the Intermap IFSAR system can be
directly referenced to the geoid without the external geoid
information. In the paper, the algorithm of determination of the
local or regional geoid from the integrated GPS/INS data is
presented. The evaluation results show that an accuracy of 2-3
mGal for the airborne gravity measurement and 5-10 cm for the
geoid, determined by Intermap IFSAR airborne gravity and
geoid mapping system, can be achieved.
The objective of this paper is to present the integrated airborne
IFSAR mapping system, developed by Intermap, for both DEM
and geoid mapping applications. An overview of the IFSAR
mapping process including the principle of the geo-coding for
3-D mapping is given in the paper. Also, the concept of
integrated airborne IFSAR mapping system will be introduced.
The roll of GPS/INS as georeferencing for the 3-D mapping, the
principle of airborne geoid mapping based on GPS/INS are also
included in the paper. The characteristics and the accuracy of
the integrated mapping system are discussed in detail. The
critical issues in mapping rural and mountain areas with limited
ground supports are included. The results from some test
examples demonstrate the capability of the integrated IFSAR
mapping system.
2. AIRBORNE IFSAR TECHNOLOGY
2.1 Principle of SAR Interferometry
3-D mapping using IFSAR system is typically based on the
principle of interferometry of two SAR images. The radar pulse
